Wide band short wave antenna and transmission line system



April 29, 1941. P. s. CARTER 2,239,700

WIDE BAND SHORT WAVE ANTENNA AND TRANSMISSION LINE SYSTEM Original FiledFeb. 15, 1938 INVENTOR PHIL/P 8. CARTER ATTORNEY Patented Apr. 29, 1941S PATENT OFFICE WIDE BAND SHORT WAVE ANTENNA AND TRANSMISSION LINESYSTEM Philip S. Carter, Port Jefferson,

Radio Corporation of America,

7 Delaware N. Y., assignor to a corporation of Original applicationFebruary 15, 1988, Serial No.

190,555. Divided and this application September 9, 1939, Serial No.294,126

7 Claims.

This application is a division of my application #190,555, filedFebruary 15, 1938, now Patent No. 2,181,870, dated Dec. 5, 1939.

The present invention relates to short wave antenna and transmissionline systems, for providing a substantially flat impedance versusfrequency characteristic over a wide range of frequencies, such as maybe encountered in television transmission or reception. Moreparticularly, the present invention relates to improvements in shortwave antenna and transmission line'sys-tems of the type described in mypreviously filed copending applications, Serial Nos. 147,817, filed June12, 1937; 187,594, filed January 29, 1938; 188,821, filed February 5,1938; and 190,939, filed February 17, 1938. In brief, the antennasdescribed in the before mentioned applications comprise conductivestructures in the form of one or more conical surfaces of revolutionhaving transmission line feeders connected to the apices thereof.

In my above-mentioned copending applications, the short wave antennasper se consist of conical surfaces of revolution to Whose apices thetransmission line feeders are connected. Since the field configurationbetween any two conical surfaces of revolution of the type described inthese applications corresponds to a spherical wave expanding from theapices of the cones out to the large ends thereof, and since the fieldconfiguration in an ordinary transmission line corresponds to a plainwave, it will be evident that at the junction points of the transmissionline and the conical antennas (i. e., their apices), there will be anabrupt change of field configuration from that corresponding to a plainwave to that corresponding to a spherical wave, and vice versa,depending upon Whether the antenna and transmission line is used as atransmitter or a receiver.

One of the objects of the present invention is to avoid the abruptchanges in the electromagnetic field configuration between thetransmission line and the short wave antenna of the type described in mycopending applications.

In order to overcome this abrupt change in field configuration betweenthe transmission line feeder and the :conical surface of revolution, Ipropose to taper my antenna, which is in the form of a conical surfaceof revolution, very gradually until the apex of the cone joins with andhas the same dimensions as the transmission line to which it isconnected. Putting it another way, I. propose to gradually increase thedimensions of the transmission lineuntil it forms part of and has thesame dimensions as the conical surface of revolution (antenna) to WhlOhit is joined.

According to one embodiment of my invention, the dimensions of thetransmission line are gradually increased, and the directions of thetransmission line conductors changed near the points of junction withthe conical surfaces of revolution. In this way, where a short waveantenna in the form of two opposed conical surfaces of revolution isemployed, the antenna and transmission line of the present invention maytake the form of a pair of metal horns, curving outwardly from oneanother in opposite directions.

Where the transmission line is of the coaxial type, it is preferred thatthe outer conductor also increase in dimensions at the correspondinglocations of increase in dimensions of the inner conductor, over somedistance, so that in effect the outer conductor has a wide mouth at thepoint of termination adjacent the antenna. The increase in dimensions ofthe outer conductor may or may not be in proportion to the increase indimensions of the inner conductor. In accordance with a particularembodiment of the invention, the coaxial transmission line has the outerconductor tapered in the form of a horn. Where two separate coaxiallines are employed to feed energy to or receive energy from a pair ofopposed conical antenna structures, the outer conductors of said twolines may take the form of horns extending in opposite directions.

A better understanding of the invention may be had by referring to thefollowing description, which is accompanied by a drawing, wherein:

Figure 1 illustrates one embodiment of my invention having a.transmission line in the form of two open parallel conductors connectedto my short wave antenna.

Figure 2 illustrates another embodiment of my invention, wherein acoaxial type of line connects with a. single conical antenna structure;and

Figure 3 illustrates a third embodiment of my invention, wherein a pairof conical antenna structures are connected to a pair of coaxialtransmission lines, in accordance with the invention.

Referring to Figure 1, there is shown a short wave antenna andtransmission line system providing a substantially flat impedance versusfrequency characteristic over a wide band of frequencies comprising apair of metal conductive antenna structures I, 2 in the form of hornsconnected to a two-conductor transmission line TL. Horns I, 2 comprise,for the major portions of their lengths adjacent; their bases (i. e.large ends) conical surfaces of revolution and for their portionsadjacent the transmission line TL tapering surfaces which graduallydecrease in dimension until they have the same dimensions as theconductors of the transmission line TL to which they are connected. Ineffect, we can say that the antenna structures I, 2 are cones distortedfrom the vertical line AA to form bent horns.

A continuous and gradual change in diameter from the transmission lineconductors TL to'the outermost ends of the horns I 2 provides a gradualchange in the electromagnetic field configuration from thatcorresponding to the planar wave emanating from the transmission line TLto that corresponding to the spherical wave emanating from the horns orcones l, 2. By

means of such an arrangement, I thus avoid any abrupt changes in thefield configuration of the transmission line and the cones I, 2 at theirjunction points.

I have found that a short wave antenna in the form of one or moreconical surfaces of revolution has a substantially constant surgeimpedance throughout its length. In a wave guide for a spherical wave,it is important that, to obtain a constant surge impedance, theconducting surfaces of the wave guide take substantially the shape ofconical surfaces of revolution. These conical surfaces of revolution maybe composed either of metallic sheet material or a plurality of wiresregularly distributed around and lying in a surface of revolution. Asfor a transmission line where the guided Wave is in the form of a planewave, the surge impedance is constant throughout the length of the lineif the ratio conductor-spacing to conductor-diameter is constant.Consequently, to obtain the same constant surge impedance heretoforeobtained both in the transmission line and the conical surface ofrevolution, I gradually increase both the spacing and diameter of theconductors of the line as the guided Wave travels from the transmissionline to the cone. This gradual increase in dimensions of thetransmission line is effected until these dimensions form part andparcel of the conical surfaces of revolution, thus obviating any abruptchanges in dimensions between the transmission line conductors and thecones.

While the foregoing theory is believed to be the correct one underlyingmy invention, it should be distinctly understood that the theoreticalexplanation is given merely for the purpose of exposition and in orderthat the invention may be better appreciated. The invention, however,does not depend upon the accuracy of this explanation and is independentof any theory to account for the results achieved.

Figure 2 illustrates another form of my invention which employs a singlehollow cone I, extending outwardly from a reflecting surface 3 which maybe the electrically conducting roof of a building, an electricallyconducting side wall of a. building, or ground. Here the transmissionline feeder TL is in the form of a coaxial conductor comprising an innerconductor 4 and an outer conductor 5, both of which are graduallyincreased in dimension at their upper ends near the apex of the cone I.The inner conductor 4, similarly as in Figure 1, gradually increases indimension until it forms part of the cone I. The outer conductor 5 iscurved away from the apex of the antenna I, and also gradually increases75 in its dimensions so as to form a larger open mouth than wouldordinarily be formed if this conductor continued straight upward. Itwill be apparent, from what has been said before, that the outerconductor 5 expands in dimensions with the expansion of the innerconductor 4, so as to obtain constant ratio of outside to insidediameters of transmission line over some length in order to obtainconstant surge impedance.

Figure 3 illustrates still another arrangement wherein a pair of opposedconductive structures I, 2 of a type substantially similar to thatillustrated in Figure 1, is energized from a pair of coaxialtransmission lines T '11.". These conical structures 2, it will benoted, are in the form of horns bent in opposite directions. The outerconductors of the coaxial transmission lines T TL" also increase indimension at the portions adjacent to the apices of the cones l, 2 so asto form horns in the manner shown in the drawing. Each of these outerconductors of the transmission line increases in diameter with theincrease injdiameter of the associated inner conductor, so as to providea substantially constant ratio of outer to inner diameter of line oversome length. It should be noted that the outer conductors of thetransmission lines of Figure 3 extend above the apices of the cones forsome appreciable length, and are then flared.

I have found that my antenna and transmission line system, asillustrated in all three figures of the drawing, give an extremely wideband impedance versus frequency characteristic.

It will be obvious, of course, that the invention is not limited to theprecise arrangements illustrated in Figures 1, 2 and 3, since variousmodifications may be made Without departing from the spirit and scope ofthe invention. For example, the conical or horn type of structuresshown, illustrated and described in the present specification may bemade either of sheet metal or of a cage of wires in the manner verygenerally shown in my copending application Serial No. 187,594, filedJanuary 29, 1938.

I claim:

1. A short wave antenna and transmission line system having a wide bandimpedance versus frequency characteristic comprising a pair ofconductive structures in the form of oppositely disposed horns, and acoaxial transmission line near each horn, the inner conductor of eachline gradually expanding in diameter until it imperceptibly merges withthe small dimension portion of its associated horn, the outer conductorof each transmission line also expanding in diameter at the location ofexpansion of the inner conductor thereof to maintain substantiallyconstant the outer to inner diameter ratio between the conductors.

2. An antenna and transmission line system in accordance with claim 1,characterized in this that each outer conductor increases in diameterand extends, for a short distance at least, beyond the apex of the hornto surround a small portion thereof, said outer conductor being flaredat its open end.

3. A short wave antenna and transmission line system in accordance withclaim 1, characterized in this that the major portions of said horns arein the form of conical surfaces of revolution whose longitudinal axesextend substantially in the same straight line, the conductors of saidtransmission lines extending substantially perpendicular to saidlongitudinal axis.

4. A short wave antenna and transmission line system comprising aconical surface of revolution extending from. an electrically conductingsurface such that the longitudinal axis of said surface of revolution issubstantially perpendicular to said surface and the apex of said surfaceof revolution is adjacent said electrically conducting surface, acoaxial transmission line connected to the apex of said surface ofrevolution, the inner conductor of said line gradually expanding indiameter until it imperceptibly merges with the apex of said surface ofrevolution, the outer conductor of said line also expanding in diameterat the location of expansion of the inner conductor, until said outerconductor merges with said conducting surface.

5. A short wave antenna and transmission line system comprising anantenna element which gradually expands for at least a portion of itslength and connected thereto a coaxial transmission line, said linehaving a gradually expanding inner conductor, the diameter of the innerconduotor of said transmission line gradually merging with the expandingantenna element.

6. A short wave antenna and transmission line system comprising a hollowconical antenna element and connected thereto at its small end a coaxialtransmission line, said line having a gradually expanding innerconductor, the diameter of the inner conductor of said transmission linegradually merging with the small end of said antenna element.

'7. A short Wave antenna and transmission line system having a wide bandimpedance versus frequency characteristic comprising a pair ofconductive structures in the form of oppositely disposed hollow horns,and a coaxial transmission line near each horn, the inner conductor ofeach line gradually expanding in diameter until it imperceptibly mergeswith the small dimension portion of its associated horn, the outerconductor of each transmission line also expanding in diameter at thelocation of expansion of the inner conductor thereof to maintainsubstantially constant the outer to inner diameter ratio between theconductors.

PHILIP S. CARTER.

